Happy chickens

A chicken who doesn’t get adequate enrichment and mental stimulation will be more inclined towards problem behaviors. Feather pecking, being noisy, bullying, egg eating ... are almost always a result of chickens that are confined without proper enrichment.
First, let’s review the basic requirements for housing chickens.
The hen house, where they lay their eggs during the day and sleep at night, should be spacious enough to accommodate everyone with minimum squabbles:

4 sqft floor space per chicken

1 nest box for every 3-4 hens

12” of roosting space per chicken

The run, where they roam during the day, should be a minimum of 10 sqft per chicken. That said, the more space they have, the happier they will be.
And make sure that everyone has access to food and water. One feeder and one waterer for 7-8 chickens is usually a good ratio, but if you see any bullying happening around these resources, just add more.
Second, maximize the following natural behaviors to make your chickens happier:
Dust-bathing. Chickens bathe in dirt to clean themselves, but it’s also a social activity they like doing with friends. Make sure your chickens always have access to dry dirt. It will definitively help with boredom. If your run is on a cement slab or similar, provide dirt in large litter boxes, cardboard boxes, or kiddy pool.
Sun-bathing. Chickens enjoy basking in sunlight and you will often see them laying on the ground with eyes closed and wings stretched. At the same time, they absorb vitamin D from the sun exposure. Sun-bathing is another group coordinated activity. Place the coop in a way that the run gets some sunshine.
Perching. Chickens like to perch as we like to sit on a chair. In addition to the roosts in the hen house, provide roosts in the run. Place them in the shade, under a tree so the predators cannot spot them from the sky.
Foraging. Chickens are foragers by nature. In the wild, they spend most of their day searching for food. Instead of serving their food on a silver plate, let’s make it a bit more challenging for them to get it. Hang the lettuce in a wire basket, spread treats on a pile of mulch, use an interactive treat dispenser (it could be a simple plastic bottle with holes in it)... Click on the image below for more ideas.

And finally make the chicken yard interesting. Design it as you would design a playground for a 2-year-old. Think about using the vertical space to provide more room and enrichment.
Provide places to explore, climb and hide. A bale of straw is a fun addition to the run, or even better a bale of hay so the chickens can forage for seeds. Branches to perch on, a hollow log to hide under, a ladder to climb... are all fun things to add in the chicken area.
Plant grass, shrubs, and trees in the area to provide food, cover, and shade. Make sure the plants are not toxic to chickens. Refresh the edibles regularly either by having a grazing frame on top of the grass, or by planting them in pots that can easily be replaced.
Put lots of mulch on the ground to encourage more foraging activity. Leaves, wood chips, straw, pine needles... are all wonderful materials for chickens to scratch in.
Add some water features, especially in the summer when temperatures are above 80°F. Do make sure it’s shallow so there is no accidental drowning! A water fountain, drip irrigation (my girls just love drinking out of the irrigation tube of our fruit trees), a soaker hose, a mister... can keep your chickens entertained and cool for hours.
After noticing that a chicken we fostered enjoyed looking at her reflection in the rim of the washing machine, we added a mirror in our chicken yard. It’s very entertaining to watch them interacting with it.
If you are still looking for ideas on how to enrich your chicken yard, here is a video of the ultimate chicken playground :)